Apoptosis is an important process in normal development and functioning of multicellular organisms. Physiological apoptosis plays an important role in various normal processes, however, abnormal apoptosis causes various diseases (Science. 267, 1456-1462 (1995); Biochem Biophys Res Commun. 266 (3), 699-717 (1999)).
For example, inhibited apoptosis may cause a cancer, an autoimmune disease, an inflammatory disease, and a virus infection. On the other hand, excessive apoptosis may cause a degenerative neurologic disease or a cardiac disease. Thus, as regulation of apoptosis in a concerned tissue or cell is very valuable, a substance promoting apoptosis is useful for preventing and treating an autoimmune disease, a lymphoproliferative disease, an inflammatory disease, and a virus infection and a substance inhibiting apoptosis is useful for preventing and treating a degenerative neurologic disease or a cardiac disease.
MicroRNAs (miRNAs) are non-coding RNAs formed when a long hairpin type transcript produced in a cell is cleaved by enzymes named as Drosha and Dicer into 19 to 25 nt. miRNAs have a base sequence which is incompletely complementary to a 3′ untranslated region of a target gene mRNA, and thus inhibit translation. However, miRNAs have a fully complementary base sequence, and thus induce mRNA degradation.
In 2004, a first case of a virus that EBV expresses its own viral miRNA was reported. Afterwards, 25 pre-miRNAs were discovered. Among the pre-miRNAs, 22 pre-miRNAs produced from a BART transcript were largely divided into Cluster 1 and Cluster 2, and were expressed in most of the EBV-related tumor or cell strain.
miR-BART5-5p, which is expressed in a EBV-infected cell, was reported to inhibit expression of PUMA, which is a pro-apoptotic protein, to increase a rate of cell survival rate (J Exp Med. 205(11), 2551-2560 (2008)). On the other hand, it was reported that, while LMP1, which is an oncogenic EBV protein, induces cell growth and transformation at a low LMP1 expression level, LMP1 inhibits cell growth at a high LMP1 expression level, and miR-BART1-5p, 16-5p, and 17-5p inhibit an LMP1 expression to decrease apoptosis (Proc Natl Acad Sci USA. 104(41), 16164-16169 (2007)). It was reported that miR-BART22-3p inhibits expression of LMP2A, which is known to be necessary to maintain EBV latency, and, although miR-BART22-3p does not affect cell growth or apoptosis, miR-BART22-3p may promote immune evasion (Neoplasia. 11(11), 1174-1184 (2009)). It was reported that miR-BART2-5p targets BALF5, which is an EBV DNA polymerase, to contribute to maintenance of EBV latency and, at the same time, targets MICB, which is a ligand of a natural killer cell, to evade an immune response by the natural killer cell (Nucleic Acids Res. 36(2), 666-675 (2008); Cell Host Microbe. 5(4), 376-385 (2009)). It was reported that miR-BART6-5p targets Dicer, which is related with miRNA biogenesis, and contributes to maintenance of EBV latency (J Biol. Chem. 285(43), 33358-33370 (2010)). Recently, it was proved through a luciferase reporter assay that miRNAs of BART Cluster 1 and Cluster 2 inhibit expression of Bim, which is a pro-apoptotic gene, and reduce apoptosis, but the specific BART miRNA having such functions was not identified (Virology. 412(2), 392-400 (2011)). As described above, EBV BART miRNAs are known to promote cell growth and inhibit apoptosis.